Hospital rooms and the like are universally equipped with patient signaling devices that allow a patient, with a minimum of effort, to signal a centralized nurse station or the like when assistance is required. Such signaling systems typically, and preferably, comprise electrically powered networks that allow the patient to signal the central station by actuating an electrical switch. A display panel at the central station indicates which patient, in which room, is signaling for assistance. The electrical current carrying portions of the network, however, must be isolated from the patient. As will be readily appreciated, the use of an electrical switch, in proximity to a patient requiring an oxygen rich environment, presents the twin hazards of explosion and fire.
U.S. Pat. No. 3,823,285, entitled Pneumatically Actuated Switching Device With Ball Contact Means, discloses a pneumatically actuated signaling device that provides for the remotely actuated, selective closing of an electrical contact switch by a patient. The switching device disclosed in the '285 patent includes a deformable bulb, squeezeable by a patient, that is connected to an electrical switching means by a hollow pneumatic tube. The electrical switching means comprises an electrically conducting, metal ball that is shiftably carried within a tubular sleeve. Collapsing the bulb causes an increase of air pressure that pushes the ball to a different position within the sleeve to complete an electrical contact.
The pneumatically actuated switching device disclosed in the '285 Dwyer patent relies on gravity to bias the shiftable, electrically conducting metal ball into its unactuated position. Moreover, the chamber which holds the shiftable ball must be vented to atmosphere to allow for free movement of the ball within the chamber. Accordingly, the switch can only operate when it is oriented in its proper, upright position, and the switch cannot be submersed in cleaning fluid when cleaning and/or, sterilization of the switch is required.